The present invention relates to transmitters for tire condition monitoring apparatuses, and, more particularly, to structures for attaching valve stems to main bodies of transmitters.
Generally, a wireless type tire condition monitoring apparatus is employed for monitoring tire conditions of a vehicle. More specifically, a transmitter is installed in each wheel, to which a tire is attached, and monitors the condition of the tire. The transmitter measures the pressure in the tire, the temperature in the tire, and the like. The transmitter wirelessly transmits data that indicate the measurements. A receiver is installed in a body frame of the vehicle for receiving the data from the transmitter.
FIG. 4 shows a prior art transmitter by way of example. The transmitter is attached to a wheel rim 110. The transmitter includes a main body 100 and a valve stem 101. The main body 100 is accommodated in a tire (not shown). The valve stem 101 projects from the main body 100 to the exterior of the tire through the wheel rim 110. The main body 100 includes a casing 102 for accommodating a pressure sensor, a signal-processing unit, and a battery (none is shown). The casing 102 has an attachment wall 103 to which the valve stem 101 is attached. The attachment wall 103 is formed integrally with the casing 102. A bolt hole 103a extends through the attachment wall 103.
An air inlet hole 104 axially extends through the valve stem 101. The air inlet hole 104 includes a threaded hole 104a. The threaded hole 104a is located at a position corresponding to the base of the valve stem 101. A bolt 105 is passed through the bolt hole 103a and is engaged with the threaded hole 104a. When the bolt 105 is fastened, the valve stem 101 is secured to the main body 100. The bolt 105 has a through hole 105a through which air flows.
A through hole 110a extends through the wheel rim 110, and the valve stem 101 is passed through the through hole 110a. A rubber grommet 106 is attached to the base of the valve stem 101 to seal the through hole 110a. The valve stem 101 is passed through the through hole 110a from the inner side of the wheel rim 110, thus projecting from the outer side of the wheel rim 110. A nut 107 is engaged with the projecting end of the valve stem 101 through a washer 108. The nut 107 is fastened to secure the valve stem 101 to the wheel rim 110. A cap 109 is engaged with the distal end of the valve stem 101.
The casing 102 accommodates a transmitter antenna for wirelessly transmitting data. The casing 102 is formed of resin such that radio wave, which is wirelessly transmitted, is not shielded by the casing 102. This structure also reduces the weight of the transmitter. However, when the bolt 105 is fastened to secure the valve stem 101 to the main body 100, a relatively great force acts on the attachment wall 103, which is also formed of resin. This may damage the casing 102.
When the vehicle is traveling, centrifugal force acts on the transmitter attached to the wheel rim 110, thus vibrating the transmitter. This may loosen the bolt 105. However, as described, if the bolt 105 is fastened with excessive force, the casing 102 may be damaged. Accordingly, the fastening force of the bolt 105 must be limited.
The fastening force of the bolt 105, which acts on the attachment wall 103, gradually distorts the casing 102 (hereinafter, the distortion of the casing 102 will be referred to as xe2x80x9ccreepingxe2x80x9d). The creeping of the casing 102 also loosens the bolt 105.
Accordingly, it is an objective of the present invention to provide a transmitter of a tire condition monitoring apparatus in which a valve stem is reliably attached to a main body in a stable manner.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, the invention provides a transmitter used in a tire condition monitoring apparatus for wirelessly transmitting data indicating a condition of a tire attached to a wheel of a vehicle. The transmitter includes a main body, a cylindrical collar, a valve stem, and a fastener. The main body is located in the tire and has an attachment portion through which an attachment hole extends. The cylindrical collar is received in the attachment hole, and the strength of the collar is larger than the strength of the main body. The valve stem projects from the main body to pass through the wheel. The fastener is fastened to the valve stem to attach the valve stem to the attachment portion of the main body. When the nut is fastened, the attachment portion and the collar are clamped between the valve stem and the fastener. The fastening force of the fastener is applied mainly to the collar.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.